The invention relates to a method of scanning objects by means of ultrasound echography, involving the repeated transmission of ultrasound signals by means of at least one ultrasound transducer and the reception of the ultrasound echoes which correspond to the principal obstacles encountered by the transmitted signals in their propagation direction, the signals received being separated into n frequency bands which are substantially equal and consecutive so that they span approximately all frequencies of the signals received, the envelope of the signals in each frequency band being subsequently determined.
The invention also relates to a device for performing such a method, including at least one ultrasound transducer which is connected to a transmitter stage for the repeated transmission of ultrasound signals and to a receiver stage for receiving the ultrasound echoes which correspond to the principal obstacles encountered by the transmitted signals in their propagation direction, said receiver stage including at least:
(A) an amplifier which receives the output signal of the transducer;
(B) a group of n channels which are connected in parallel to the output of the amplifier and each of which successively includes:
(1) a bandpass filter, the group of n filters thus formed being such that their respective passbands are substantially equal and consecutive so that they span substantially the passband of the transducer;
(2) an envelope detector which is identical for each channel and which includes a rectifier which is succeeded by a lowpass filter. Such a device can be used, for example for the non-destructive testing of materials and the scanning of biological tissues.
A conventional ultrasound echographic image is obtained by the detection of the envelope of the echoes produced in the tissues by an ultrasound beam. Because the most important echoes arise at the boundaries of the organs, these images mainly show the contours thereof. All information concerning the phase (and hence the frequency) of the signal is then lost. Such information can be related to suitable indicators of some indistinct diseases which are difficult to diagnose by other means.
It is an object of the invention to provide a method of and a device for scanning objects by means of ultrasound echography in which the frequency-dependency of the scatter function of the object scanned can be determined. This method enables a quantitative determination of the scatter function of the object examined which can be characterized by this function so that the pathological condition thereof can be determined.
To this end, the method in accordance with the invention is characterized in that each of the signal envelopes, being proportional to the power spectrum of the echographic signal, is divided by a dividing signal which is proportional to the power spectrum of a phantom having the same attenuation as the object scanned, the logarithm of the signal resulting from this division being determined, after which the following operations are performed in the channels a, b, . . . , i, . . . , n on the basis of the signals thus obtained;
(a) calculating the logarithm of the central frequency f.sub.i of the passband associated with each channel or of another frequency which is representative of this passband;
(b) storing in a memory and/or displaying a function of the ratio of the scatter function of the object examined and that of the phantom as a function of the frequency mentioned with reference to the calculation performed sub (a) as a representation of the subject's scatter function;
The device for performing the method in accordance with the invention is characterized in that the receiver stage also includes, connected behind the envelope detector; in each channel:
(3) a divider circuit, a first input of which receives the output signal of the corresponding envelope detector and a second input of which receives a dividing signal which originates from a first memory which is controlled by a clock circuit which is activated by the clock of the transmitter stage;
(4) a logarithmic amplifier; the receiver stage also including an arithmetic circuit which is connected to the output of the n channels and which performs the following operations on the basis of the n output signals of the channels:
(a) calculating the logarithm of the central frequency f.sub.i of the passband associated with each channel or of another frequency which is representative of this passband;
(b) storing in a memory and/or displaying a function of the ratio of the scatter function of the object scanned and that of the phantom as a function of the frequency mentioned with reference to the calculation performed sub (a) as a representation of the subject's scatter function.